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35.4 Variable naming

The recommended variable naming is to follow C/C++ naming conventions, in which variables are lowercase, with the underscore character (_) used as a separator. Thus it is preferred to use sigma_y, rather than the run together sigmay, camel-case sigmaY, or capitalized camel-case SigmaY. An exception is often made for terms appearing in mathematical expressions with standard names, like A for a matrix.

Another exception to the lowercasing recommendation, which follows the C/C++ conventions, is for size constants, for which the recommended form is a single uppercase letter. The reason for this is that it allows the loop variables to match. So loops over the indices of an $M \times N$ matrix $a$ would look as follows.

for (m in 1:M) {
  for (n in 1:N) {
     a[m, n] = ...
  }
}